This invention relates to a pipe cluster unit formed of individual plastic pipes having a smooth or wavy inner circumferential wall and a method of making the pipe cluster unit. The individual pipes are, after their manufacture, combined into a pipe cluster unit such that at least two adjoining pipes are in a longitudinal linear engagement with one another.
A pipe cluster unit of the above-outlined type is disclosed, for example, in German Offenlegungsschrift (application published without examination) No. 3,045,388. This publication discloses an apparatus for laying communication cables with light wave conductors in the ground. The communication cables with the light wave conductors are introduced (pulled) into a previously manufactured pipe cluster. The pipe cluster is formed of individual plastic pipes and is combined into a unit by stranding together the individual pipes. The known method of stranding such a cluster is, according to the above-noted publication, effected with a large pitch to ensure that upon introduction of the cable into the pipes no large frictional forces are generated. According to the known prior art it is further feasible to combine parallel plastic pipes into a unit by attaching them to one another with mechanical securing elements. The unit may be additionally surrounded by a jacket.
Stranded pipes extend helically in the pipe cluster. Even in case of large-pitch strands difficulties have been experienced during the introduction of the cable into such pipe clusters along substantial lengths.
While the above-noted pipe securing elements permit a twist-free arrangement of the pipes in the cluster, they extend necessarily at least in part beyond the outer circumference of the externally located individual pipes and thus increase, at least in sections, the outer diameter of the pipe cluster. This may be of significant disadvantage particularly in case the pipe cluster is to be surrounded by a common jacket. Such jacket is, as a rule, a cable-protecting pipe which may have been previously laid. The known pipe cluster is then introduced into the cable-protecting pipe. The projecting parts of the mechanical securing elements may cause difficulties during this operation. In addition, because of the projecting mechanical securing elements, the individual pipes must have a'correspondingly smaller diameter or a lesser number of individual pipes must be used which is disadvantageous for an optimal utilization of the pipe cluster.
German Gebrauchsmuster (utility model) No. 8,213,407.3 discloses a pipe cluster which is formed of plastic pipes and which is intended for introduction into a cable duct. The pipe cluster is formed of a plurality of individual pipes combined into a mat by means of spacer webs which form integral, one-piece parts of the pipes. The spacer webs are flexible and permit a relative positioning among the individual pipes such that the adjoining pipes are longitudinally in a linear contact with one another. The pipes connected to one another by means of the spacer webs are pulled into a cable duct in an inwardly pivoted condition. During this operation, however, difficulties are experienced because the inward pivoting of the pipes has to be effected at the point of introduction into the cable duct and thus an appropriate apparatus is required at that location. Further, risks are high that the loose arrangement of the outer pipes after a pivotal motion of the pipes leads to such a flexibility of the pipe cluster that, particularly for substantial lengths, an insertion of the pipe cluster into a cable duct is not possible. In such a prior art structure a firm bond of the tubes in the cluster is missing altogether which leads to difficulties in introducing the pipe cluster into a cable duct. If, in order to eliminate this disadvantage, mechanical securing members are used for the pipes, the already noted disadvantages will apply. The pipe mat formed according to the prior art is also disadvantageous in that substantial lengths thereof cannot be wound on a drum. Thus, cable guide pipes combined into a pipe mat are not well adapted for insertion into cable protecting pipes already installed. Further, it is not feasible to directly install the pipe mat into the ground because the flexible spacer webs between the individual pipes do not permit a pipe laying in a single plane.